Intake and/or exhaust gas sensors may be operated to provide indications of various gas constituents. Output from an oxygen sensor, for example, may be used to determine the air-fuel ratio (AFR) of exhaust gas. An oxygen sensor may be disposed in an engine intake passage to determine the concentration of exhaust gas recirculation (EGR) gasses in intake charge air. Indications of AFR may be used to adjust various engine operating parameters such as fueling and a target AFR, for example. In particular, exhaust gas AFR may be controlled to achieve the target AFR in order to maximize operating efficiency of an emission control device. An oxygen sensor may alternatively or additionally be used to detect ambient humidity, with one or more engine operating parameters being adjusted based on the detected ambient humidity.
In some approaches, an oxygen sensor is used to detect ambient humidity during engine non-fueling conditions such as deceleration fuel shut-off (DFSO). As the ingestion of hydrocarbons by the oxygen sensor, resulting for example from flow of positive crankcase ventilation (PCV) gasses, may confound ambient humidity measurement and degrade aspects of engine operation based thereon, an intake throttle of the engine may be opened to reduce PCV flow and increase ambient airflow.
The inventors herein have recognized an issue with the approach identified above. Specifically, a transmission may downshift during coast down during DFSO. When performing the shift while the engine operates under relatively high load, drivability of an associated vehicle may be degraded and/or noise, vibration, and harshness (NVH) may occur.
One approach that at least partially addresses the above issues includes a method of operating an internal combustion engine comprising deactivating at least one engine cylinder, performing a diagnostic while the at least one engine cylinder is deactivated and while the engine is operating under high load, predicting a transmission shift, and responsive to the predicted transmission shift, reducing engine load below the high load and terminating the diagnostic.
In a more specific example, predicting the transmission shift includes determining whether a transmission shift request flag has been set in an engine controller, the flag indicating whether the transmission shift will occur.
In another example, the diagnostic detects ambient humidity via an oxygen sensor. In this way, degraded drivability and/or NVH may be reduced or obviated when performing a transmission shift following non-fueling conditions, while allowing ambient humidity to be detected under suitable conditions. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.